1. Field of the Invention
The present invention relates to methods and apparatus for cleaning deposits from a semiconductor wafer. More particularly, the present invention relates to the cleaning of deposited films and flakes from the edge portions of a semi-conductor wafer during the manufacture of semiconductor integrated circuits.
2. Description of the Related Art
Semiconductor wafer fabrication involves a series of processes used to create semiconductor devices and integrated circuits (ICs) in and on a semiconductor wafer surface. Fabrication typically involves the basic operations of layering and patterning, together with others such as doping, and heat treatments. Layering is an operation used to add thin layers of material (typically insulator, semi-conductor or conductor) to the surface of the semiconductor wafer. Patterning is an operation that is used to remove specific portions of the top layer or layers on the wafer surface.
Once the integrated circuits on the wafer are completed, i.e., layering and patterning are implemented, the wafer is conventionally sliced into sections known as die. A large number of wafers are diced from a wafer, typically 100 to 1000. A wafer may comprise as many as 10 or more layers, each layer formed in a separate step. During processing of semiconductor wafers, films (i.e., layers) are deposited not only on the selected areas of the wafer surface designated for the die, but also on the margin of the wafer, i.e., the wafer edge and the bevel. The films may also be deposited on the backside of the wafer near the edge. These films located at or near the edge may become problematic during subsequent processing, such as occurring when the edge deposits begin to flake off. This may result in contamination during subsequent process steps. For example, such flakes may cause a bridge between two conductors or prevent the formation of a pattern. The flaking may therefore cause processing defects which may result in die failure at test.
The existing methods for resolving these problems are time consuming and expensive. One method involves etching away the outside edge area of the wafer by performing an additional etch processing step. For example, a separate resist coating, patterning, and etching step is often used to “clear” the edge portion of the wafer. This step is expensive, and often the equipment used is designed for high precision layouts. Such precision is unnecessary for low precision edge clearing work and hence adds to the cost of fabricating the wafer. In addition, steps are also included in the process that are specifically designed for wafer backside cleaning.
The front side, edge, and backside cleaning steps are typically performed in a wet process etch. But the existing techniques are not always effective in removing all deposits. Any films remaining on the edge of the wafer will tend to flake off. Moreover, wet processing requires the use of very expensive wet process tools. Wet cleaning of the wafers is also labor intensive and hazardous to the workers. Waste generated from the process is difficult and expensive to deal with.
Unfortunately, there is no conventional process that is currently specifically directed to removing films from the edge and bevel of the wafer. Accordingly, it is desirable to provide a more effective method and apparatus for removing films from the bevel and edge of a wafer.